Lithium soap grease



Patented June 13,1944

umrao STATES, PATENT 'OFFICE LITHIUM. soar cams]:

poration of Delaware No Drawing. Application November 15, 1942, SerialN0. 468,068

12 Claims.

This invention relates to a stable low temperature grease. Moreparticularly, it deals with a lithium soap grease comprising a smallamount of an oxidation inhibitor, and a low viscosity and low pour pointmineral oil having a viscosity gravity constant (V. G. C.) of greaterthan .84.

The V. G. C. is an arbitrary constant calculated from the SayboltUniversal viscosity of an oil and its specific gravity, the value ofwhich constant increases with the naphthenicity, and decreases with theparaihnicity of the oil (see the article by Hill and Coats in vol. 22,1928, pp. 641-4, Ind. Eng. Chem, entitled Viscosity Gravity Con stant ofPetroleum Lubricating Oils). Pennsylvania oils, typical of parafiinicoils, have V. G. C.s of about .80, while typical naphthenic oils have V.G. C.s above about .84 up to about .90.

Investigations into the flow properties of greases at low temperatureshave revealed in the past that the flow of greases is primarily afunction of the viscosity of the oil at that temperature and, to alesser extent, of the amount and type of soap employed. Since oils oflow V. G. C. change less in viscosity of a given temperature range thanoils of higher V. G. C., such oils have in the past been employed forlow temperature operation. Concerning the influence of the soap, it isknown that relatively small amounts of soap are preferred to preservethe flow properties of the oil, and that lithium soap greases havebetter flow properties at low temperatures than comparable greases madewith other soaps.

Lithium soap greases must contain free fatty acid to prevent excessivegelling. Such low temperature greases as were produced heretoforeemploying oils having S. U. viscosities below 100 sec. at 100 F.normally contain at least about .5% free acid calculated as stearicacid.

It is usually considered that low temperature greases should haveconsistencies of between about 200 and 370 A. S. T. M. penetration at 77F. By low temperatures as herein stated, we mean temperatures low asabout -100 F.

It has now been discovered that an improved low temperature lithium soapgrease can be produced by using a naphthenic oil rather than aparafiinic oil. The new lithium soap grease of this invention differsfrom the previous lithium soap greases having the same consistency andequally good physical properties in that the grease of this inventionrequires only about /2 the amount of soap and less than A the amount offree fatty acid used in previous lithium soap low temperature greases.

The reduced amount of lithium soap employed Ill in the grease of thisinvention is of material economic advantage, since lithium soap is veryexpensive. Also, the reduced amount of soap counteracts the advantage oflow V. G. C. oils employed in other lithium soap greases, because themore soap a grease contains the less it preserves the flow properties ofthe oil contained in it.

Furthermore, the amount of free fatty acid in this new grease iscritical in that an excess of acid over the amount later specifiedcauses the grease to become too soft, and when the grease is too soft,more soap must be added-which defeats one of the main advantages of thisinvention, namely, that of employing a smaller amount of soap.

These differences and advantages of the lithium soap grease of thisinvention are based upon the peculiar and unexpected influence ofnaphthenic mineral oils having a V. G. C. greater than .84 on theability of the lithium soap to produce a grease of a given consistency.

It is a primary purpose of this invention to produce an economical lowtemperature lithium soap grease which meets the rigid Army and NavyAeronautical Specification AN-G-3. Another purpose is to produce astable lithium soap grease having an efiective lubricating temperaturerange of between about 100 F. and +300 F. A further purpose is toproduce a smooth homogeneous lithium soap grease having a low soapcontent and a low free fatty acid content.

The composition of the grease of this invention may be summarized asfollows:

Greases of the above composition have consistencies as measured by theA. S. T. M. penetrometer of between about 200 and 370+.

Suitable lithium soaps consist essentially of or comprise predominantlysalts of lithium with fatty acids having 12 or more carbon atoms. In

addition, the lithium soap may contain minor amounts of fatty acid saltsof other metals, particularly Na, K, Ca, Ba, Zn, Al, etc.

Saturated fatty acids preferred in the manu facture of the lithium soap,as well as for making up the free fatty acid content of the grease, are,for example, lauric, myristic, palmitic,

stearic, arachlc, behenic, hydroxy stearic, etc. Unsaturated fatty acidswhich may be present comprise oleic, ricinoleic, etc.

Lithium soaps may be manufactured by conventional methods, e. g. bysaponification of vari- An oxidation inhibitor is essential to producean oxidation-stable grease. Some lubricating oil oxidation inhibitorsare more efiective than others in this grease. Specifically, it has beendiscovered that N-alkyl para-phenylene diamine inhibitors and condensedpolynuclear aromatic mono-amine inhibitors are the most effective.

The N-alkyl para-phenylene diamine inhibitors have the advantage of verymaterially increasing the oxidation stability and life of the grease.Such inhibitors are N-butyl para-phenylene diamine, N-N'-dibutylpara-phenylene diamine, etc. The condensed polynuclear aromaticmonoamine inhibitors do not produce a grease having quite so long a lifeas the same amount of the N-alkyl para-phenylene diamine. Suchinhibitors are pha or beta naphthylamine, alpha-alpha, betabeta, oralpha-beta dinaphthylamine, etc. er'al of these inhibitors have theadvantage of slightly increasing the consistency of the grease. Othersuitable inhibitors are mixed petroleum alkyl phenols boiling from about200 C.-240 C.

Some oxidation inhibitors which are less effective in the grease of thisinvention are: diphenyl amine, t-etra-methtyl-aminol diphenyl methane,2.4-di-tertiary butyl G-methyl phenol, and some sulfurandphosphorus-containing inhibitors.

The naphthenic mineral oils suitable for making the low temperaturelithium soap grease of this invention, as stated above, are those havinga low viscosity, low pour point and a V. G. C. of greater than .84. Suchoils are generally lubricating oils obtained from Gulf Coast,California, Venezuela and similar crudes. The pour point must be belowabout 60 F. and the S. U. V. at 100 F. usually less than 100 seconds andpreferably between about 50 and 90 seconds. Oils of S. U. V. of about 30seconds at 100 F. are too light to be considered lubricating oils.

Other ingredients which may be added include various corrosioninhibitors, extreme pressure additives, anti-wear agents, stabilizers,V. 1. improvers, and the like, provided they do not interfere with thelow temperature operation and oxidation stability of the grease.

Some extreme pressure additives which may be used comprise: esters ofphosphorus acids such as triaryl, alkyl hydroxy aryl, or aralkylphosphates, thiophosphates, or phosphites, etc.; neutral aromatic sulfurcompounds of relatively high boiling temperatures such as diarylsulfides, diaryl disulfides, alkyl aryl disulfides, e. g. diphenylsulfide, diphenol sulfide, dicresol sulfide, dixylenol sulfide, methylbutyl diphenol sulfide, dibenzyl sulfide, corresponding diandtri-sulfides, etc.; sulfurized fatty oils or esters of fatty-acids andmonohydric alcohols, e. g. sperm oil, jojoba oil, etc., in which thesulfur is strongly bonded; sulfurized long-chain olefins such as may beobalpha or beta naphthylamine', phenyl altained by dehydrogenation orcracking of wax; sulfurized phosphorized fatty oils or acids, phosphorusacid esters having sulfurized organic radicals, such as esters ofphosphoric or phosphorus acids with sulfurized hydroxy fatty acids;chlorinated hydrocarbons as chlorinated parailins, aromatichydrocarbons, terpenes, mineral lubricating oils, etc.; or chlorinatedesters of fatty acids containing the chlorine in position other thanalpha position.

Additional ingredients other than extreme pressure additives maycomprise anti-wear agents such as oil-soluble urea or thio-ureaderivatives, e. g. urethanes, allophanates, carbazides, carbazones,etc.; or rubber, poly-isobutylene, polyvinyl esters, or other highmolecular weight oil-soluble polymers to improve the stability of thegrease;

or pour point depressors to further lower the pour 7 point of the oil;or stabilizer to reduce bleeding such as glycerine (less than .1% byweight); and V. I. improvers such as poly-isobutylenes of molecularweights-above about 800, volatilized paraflin wax, unsaturatedpolymerized esters of fatty acids, and monohydric alcohols and otherhigh molecular weight oil-soluble compounds.

Example I A low temperature grease according to this invention wasprepared by a process comprising making a slurry in an open kettle oflithium stearate and distillate oil having a Saybolt Universal viscosityat F. of 62 sec., a pour point of 75 F. and a V. G. C. of .8468. Theslurry was continuously agitated and heated to a temperature of about375 F. At this temperature phenyl alpha naphthylamine was added to thegrease. The temperature of the resulting mixture was then brought up tobetween about 385 F. and 400 F. for a period of about 15 minutes andthen the grease was drawn from the kettle and cooled as quickly aspossible in open pans one inch deep. The cooled grease was then workedto remove any lumps that might be present therein. Amounts of theingredients were such that the composition of this grease was asfollows:

Per cent by weight Lithium stearate 7.00 Free stearic acid .02 Phenylalpha naphthylamine .20 Mineral oil 92.78

This grease was a smooth, non-corrosive, lightcolored, homogeneousgrease having a consistency of about 275 as measured by the A. S. T. M.grease penetrometer. At the end of 50 hours it bled less than 1.5% andwas tested to be an effective lubricant at temperatures as low as -67 F.

Example II Eight other samples of such lithium soap greases weresimilarly prepared, containing (1 no amine, (2) .1% and (3) .25% phenylalpha naphthylamine; (4) .1% and (5) 25% phenyl beta naphthylamine; (6).1% N-N-dibutyl paragauge measures the pressure. The time required isrecorded for the pressure to drop due to adsorption of the oxygen by thegrease. The following table shows the results obtained on these samples:

Per cent Sample (lonsist- Lbs./m. Hours N o. mhlbltopused ency pres.drop time I 290 5 3 2 Phony] alpha 1 266 100 naphthylamine. 2g g 238 a262 450 4 Phenyl beta .1 282 5 85 naphthylamine. 0 100 S ti t 5 u ygara-phenyiene .l 241 1 8 e. c 7 Alkyl phenols, .l 250 5 78 $321, 12.200 C.- s ..do .25 279 The oxidation stability limits allowed by theArmy and Navy Aeronautic Specification AN-Gqi for low temperature greaseare 5 pounds p. s. i. drop in pressure after 100 hours of oxidation.Thus, samples 2, 3, 5, 6 and 8 meet these requirements.

The low temperature greases of this invention are particularlyapplicable for lubricating mechanisms, including ball bearings, that areused in cold climates as well as mechanisms of transportation includingaircraft which operate within short periods of time between tropicaltemperatures at sea level and subzero temperatures at high altitudes.

We claim as our invention:

' .1% and 1% by weight 1. A low temperature grease consistingessentially of a hydrocarbon oil having a V. G. C. greater than .84 anda, pour point below 60 F., and containing between about 3% and 10% byweight of a lithium soap of a fatty acid of 12 or more carbon atoms,between about .01% and .5% by weight of free fatty acid having 12 ormore carbon atoms and between about .01% and 2% by weight of anoxidation inhibitorxselected from the class consisting of N-alkylatedpara-phenylene diamines and polynuclear aromatic amines.

2. The grease of claim 1 wherein the soap is lithium stearate.

3. The grease of claim 1 containing between about 6% .and 9% by weightof said lithium soap.

4. The grease of claim 1 containing between .03% and .2% by weight ofsaid free fatty acid.

5. A low temperature grease stable to oxidation consisting essentiallyof a hydrocarbon oil having a V. G. C. greater than .84, a pour pointbelow -60 F. and an S. U. V. at 100 F. of less than 100 seconds, andcontaining between about 3% and 10% by weight of a'lithium soap of afatty acid of 12 or more carbon atoms, between .01% and .5% by weight offree fatty acid having 12 or more carbon atoms. and between about .01%and 2% by weight or an oxidation inhibitor.

6. The grease of claim-5 wherein the oxidation inhibitor is selectedfrom the class of N -a1kylated para-phenylene diamines and polynucleararomatic amines.

7. The grease of claim 5 wherein the oxidation inhibitor is phenyl alphanaphthylamine.

8. The grease of claim 5 wherein the oxidation inhibitor is phenyl betanaphthylamine.

9. The grease of claim 5 wherein the oxidation inhibitor is N-N'-dibutylpara-phenylene diamine.

10. The grease of claim 5 containing between of said oxidationinhibitor.

11. The grease of claim 5 wherein the hydrocarbonoil has an S. U. V. at100 F. of between about and 90 seconds.

12. A low temperature grease consisting essentially of a hydrocarbon oilhaving a V. G. C. reater than .84 and a pour point below F., andcontaining between about 6% and 9% by weight of a lithium soap of afatty acid of 12' or more carbon atoms and between about .01% and .5% byweight of free fatty acid having 12 or more carbon atoms.

HAROLD A. WOODS. JACOBUS M. PLAN'IFEBER.

